"We have very hot temperatures forecast that could see quite a number of records broken," Ms Wilson said.

The "long list of potential record-breakers" includes Clare, north of Adelaide, that previously recorded a maximum all-time temperature of 43.7C. Clare is expected to reach 45C today.

Cummins, on the Eyre Peninsula, is expected to reach 47C, breaking a previous record of 46.2C, and Roseworthy, north of the capital, could break its previous record high of 46.7C. Temperatures there will top out at 47C during midafternoon.

Adelaideis forecast to hit 45C on Thursday, but the Bureau says the city's 80-year-old record high of 46.1C is within reach.

The hottest temperatures are expected to be recorded at Port Augusta, 300km north of Adelaide, where it could get as hot as 49C.

Adelaide residents sweltered through uncomfortable overnight lows of just 31.1C. It was 33C at 3am.

The record-high temperatures today come with elevated fire risk and warnings are in place across the state. CFS state duty commander Yvette Dowling said the soaring temperatures will be unmanageable in many parts of the state.

"If a fire does start with these forecast weather conditions, we're not going to be able to control that fire," she said.

She urged the public to avoid risky behaviour in order to minimise the bushfire threat.

"The communities are at risk, our firefighters are at risk, all emergency services are at risk tomorrow."